Free-flowing agglomerated nonionic surfactant detergent composition and process for making same

ABSTRACT

A free-flowing agglomerated powder detergent process and the resulting composition includes from about 5% to about 80% of an alkali metal carbonate; from about 5% to about 50% of a detergent surfactant, and, up to about 25% of an alkali metal salt of a carboxylic acid, wherein the carboxylic acid is selected from the group of carboxylic acids that, below a first temperature, have a greater water solubility than the water solubility of its corresponding alkali-metal salt. The alkali metal salt is preferably provided solely by the reaction of (a) a premix comprising the alkali metal carbonate coated with the surfactant (b) a carboxylic acid selected from the group consisting of citric acid, malic acid, and mixtures thereof, and (c) water.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a free-flowing agglomerated powderdetergent containing high levels of nonionic surfactant and a processfor making the same.

2. Discussion of Related Art

There is an on-going effort to provide powdered laundry detergentshaving an increased amount of detergent surfactants. The benefits ofhighly concentrated detergents include a savings in packaging use andcost. Unfortunately, there are limits to the amount of detergentsurfactant that can be included in a powdered detergent while stillproviding the consumer desired characteristics of flowability,solubility, cleaning and whitening performance.

Most granular detergents are produced by spray drying. This processinvolves mixing detergent components such as surfactants and builderswith water to form a slurry which is then sprayed into a hightemperature air stream to evaporate excess water and to form bead-typehollow particles. While spray drying the detergent slurry produces ahollow granular detergent having an excellent solubility, extremelylarge amounts of heat energy are needed to remove the large amounts ofwater present in the slurry. Another disadvantage of the spray dryingprocess is that because large scale production equipment is required, alarge initial investment is necessary. Further, because the granulesobtained by spray drying have a low bulk density, the granule packagingvolume is large which increases costs and paper waste. Also, theflowability and appearance of the granules obtained by spray drying maybe poor because of the presence of large irregularities on the surfaceof the granules.

In addition to these characteristic processing and product problemsassociated with the spray drying process, volatile materials, such asnonionic surfactants, are emitted into the air when processed by thismethod. This volatilization problem, manifested by the discharge ofdense “blue” smoke from the spray tower, is referred to as “pluming.”Air pollution standards limit the opacity of the plume. Consequently, itis necessary to limit the capacity of the spray tower or, in extremeinstances, discontinue operation.

In an attempt to avoid the problems caused by spray drying, considerabledevelopmental effort has focused on post-dosing the product withnonionic surfactants after the spray drying operation. Unfortunately,post-dosing of the spray dried base with surfactant in amountssufficient to provide satisfactory wash performance generally results ina product that has poor dissolution characteristics. Accordingly, theamount of surfactant that may be employed in the detergent formulationis severely limited. Because heavy-duty laundry detergents need largeamounts of nonionic surfactant present, inorganic silicates have beenadded to these detergent formulations to absorb the nonionic liquids.

For example, U.S. Pat. No. 3,769,222 to Yurko et al. discloses mixingliquid nonionic surfactants with sodium carbonate until partialsolidification occurs followed by the addition of large amounts ofsilica (silicon dioxide) to produce a dry free-flowing detergentcomposition. A disadvantage to this technique, however, is that becausethe silica has no significant cleaning activity, its inclusion in adetergent formulation in large amounts merely serves to increase thecost of the product. Further, the use of silica in detergents adds tothe total suspended solids (TSS) content of laundry waste water contraryto the dictates of many local and state water pollution standards.Therefore, there is an incentive to keep low the amount of silica addedto the detergent composition.

U.S. Pat. No. 4,473,485 to Greene reports that a free-flowing granulardetergent can be prepared by mixing a polycarboxylic structuring agentsolution with a micronized carbonate followed by the addition to themixture of a nonionic surfactant and water, followed by removal of theexcess water. The preferred micronized carbonate is calcium or sodiumcarbonate. A disadvantage of this process, however, is that themicronized carbonate used by Greene to enhance the flowability of thedetergent product is quite expensive as compared to standard sodiumcarbonate. Without the use of the micronized carbonate, Greene's productwould not have such good flowability. In addition, where the micronizedcarbonate is calcium carbonate, the building capability of the detergentis reduced.

Therefore, a need exists for a process and its resulting compositionthat substantially overcomes the problem of free-flowability in highlyloaded nonionic detergents.

SUMMARY OF THE INVENTION

The present invention relates to a free-flowing agglomerated detergentpowder that contains a high level of nonionic detergent surfactant and aprocess for making it. More broadly, the present invention relates to afree flowing agglomerated detergent powder that contains high levels ofdetergent surfactants and a process for making the free flowingdetergent powder. The present invention also relates to a process formaking a free-flowing agglomerated detergent powder, particularly onethat contains a high level of nonionic detergent surfactant. The methodincludes the steps of loading an alkali metal carbonate with asurfactant selected from the group consisting of anionics, nonionics,ampholytics, cationics, zwitterionics, and mixtures thereof to form ahomogeneous coated alkali metal carbonate premix; admixing a carboxylicacid into the premix; introducing water onto the mixture; and agitatingthe mixture to accomplish agglomeration. Preferably, the mixture is fedto a rotating agglomerator where a minor amount of water is sprayed intothe mixture as the agglomerator rotates. The agglomerate is preferablydried to remove the excess water, i.e., water not bound as the hydrate,to form the free-flowing detergent composition of the present invention.

Optionally, minor amounts of other known detergent ingredients may bepresent in the premix. For example, minor amounts of silicas andcarboxymethylcellulose can be mixed with the alkali metal carbonateprior to being loaded with the surfactant.

Preferably, the process includes loading sodium carbonate with asurfactant to form a homogeneous surfactant coated alkali metalcarbonate premix. The surfactant is selected from the group consistingof anionics, nonionics, zwitterionics, ampholytics, cationics, andmixtures thereof. Preferably, the surfactant is a nonionic surfactant. Acarboxylic acid that is selected from the group of carboxylic acidsthat, below a first temperature, have a greater water solubility thanthe water solubility of Its corresponding alkali-metal salt is admixedwith the premix to form a mixture. As will be discussed below, the firsttemperature is from about 15° C. to about 40° C. Preferably, thecarboxylic acid is selected from the group consisting of citric acid,malic acid, and mixtures thereof. The mixture is agitated while a minoramount of water, less than about 7%, is incorporated into the mixturecausing the carboxylic acid to solubilize and neutralize forming thesodium salt of the carboxylic acid and causing the mixture toagglomerate. The agglomerated mixture is dried to remove at least about50% of the added water to form a free-flowing powder detergentcomposition.

The resulting agglomerated detergent comprises an alkali metal carbonatepresent in about 5% to about 80% weight of the final product; adetergent surfactant, preferably, a nonionic detergent surfactantpresent in about 5% to about 50% by weight of the final product; and upto about 25% of an alkali metal salt of a carboxylic acid, wherein thecarboxylic acid is selected from those carboxylic acids that, below afirst temperature, have a greater water solubility than the watersolubility of its corresponding alkali-metal salt. As will be discussedbelow, the first temperature is from about 15° C. to about 40° C.

Preferably, the agglomerated detergent powder of the present inventioncomprises from about 5% to about 80% sodium carbonate, from about 5% toabout 50% of a nonionic detergent surfactant, wherein the nonionicsurfactant is the sole detergent surfactant present, and from about 4%to about 18% of the sodium citrate, sodium malate, and mixtures thereof.

More preferably, the agglomerated detergent powder of the presentinvention comprises from about 20% to about 70% of sodium carbonate,from about 20% to about 40% of a nonionic detergent surfactant whereinthe nonionic surfactant is the sole detergent surfactant present; andfrom about 5% to about 13% of a substantially completely neutralizedcarboxylic acid selected from the group consisting of sodium citrate,sodium malate, and mixtures thereof, wherein the sodium citrate orsodium malate is formed by the reaction, upon the addition of water,between a premix comprising (a) the nonionic surfactant and sodiumcarbonate and (b) admixed citric acid, malic acid, or mixtures thereof.

The term “coated” is used in the specification and claims to mean thatthe surfactant is present on the surface of the carbonate (and otherparticles) as well as within the carbonate (and other particles), e.g.by absorption.

Preferably, the process includes mixing sodium carbonate (and,optionally, other detergent ingredients) and a nonionic surfactant toform a homogeneous nonionic surfactant coated sodium carbonate premix,wherein the nonionic surfactant is the sole surfactant present in thepremix a carboxylic acid selected from the group consisting of citricacid, malic acid, and mixtures thereof is admixed with the premix toform a mixture. The mixture is agitated while water is incorporated intothe mixture causing the carboxylic acid to solubilize and neutralize toform the sodium salt of the carboxylic acid and to cause the mixture toagglomerate. The agglomerated mixture is dried to form a free-flowingpowder detergent composition.

The term “free water” is used in the following specification and claimsto indicate water that is not firmly bound as water of hydration orcrystallization to inorganic materials.

Unless specifically noted, all percentages used in the followingspecification and claims are by weight of the final product.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

The present invention provides a free-flowing agglomerated detergentpowder that contains a high level of surfactant, particularly a nonionicsurfactant.

The present invention also provides for a process for making afree-flowing agglomerated detergent powder that contains a high level ofsurfactant particularly a nonionic surfactant. The method includesloading an alkali metal carbonate (and, optionally, other detergentingredients) with a surfactant to form a premix comprising a homogeneousmixture of surfactant coated carbonate. A carboxylic acid is admixedwith the premix to form a mixture. The carboxylic acid is preferablyselected from those carboxylic acids that, below a first temperature,have a water solubility that is greater than the water solubility of itscorresponding alkali-metal salt. The mixture is introduced into a mixer,preferably a rotating drum agglomerator, where water is introduced tothe mixture causing the carboxylic acid to solubilize and react with thealkali metal carbonate to form the alkali metal salt of the carboxylicacid at a temperature lower than the first temperature and to cause themixture to agglomerate into particles. The particles are dried andsized.

The detergent composition comprises three essential ingredients: analkali metal carbonate, a nonionic surfactant and a substantiallycompletely neutralized carboxylic acid.

The alkali metal carbonate is preferably sodium carbonate for reasons ofcost and efficiency. Among the preferred sodium carbonates used in thefollowing examples are light density (LT) soda ash (Solvay process),mixtures of light density (LT) and medium density soda ash(Sesquicarbonate process), a special high porosity “medium-light” ash(Sesquicarbonate process) and mixtures of light density and“medium-light” ash. These particles of sodium carbonate have an averagedensity of from about 0.5 to about 0.7 and an average mesh size rangingfrom about 20 to about 200, U.S. Standard Sieve number. Carbonates suchas these are commercially available from FMC Corp. and General Chemicaland are relatively inexpensive as compared to more processed carbonatesbecause they do not require further processing such as grinding.

The sodium carbonate can be present in the free-flowing detergentcomposition in the amount of about 5% to about 80% by weight of thefinal product. The amount of sodium carbonate added to the final productis balanced against the amount of nonionic surfactant which will beloaded into the sodium carbonate as well as the amount which will beneutralized by the admixed carboxylic acid. The preferred range for thesodium carbonate is from about 20% to about 70%, more preferably fromabout 30% to about 65% by weight of the final product. It should bementioned that within the preferred range the higher levels tend to berequired under conditions of use at low product concentrations, as iscommonly the practice in North America, and the converse applies underconditions of use at higher product concentrations, as tends to occur inEurope.

If desired, the alkali metal carbonate can be mixed with other minoramounts, not to exceed about 10% of the final product, of detergentingredients before the nonionic surfactant is added to it.Alternatively, the nonionic surfactant can be added to other minoramounts of detergent ingredients, not to exceed about 10% of the finalproduct, after which they can be mixed with the nonionic surfactantcoated alkali metal carbonate. In one embodiment, the carbonate,optional detergent ingredients, and surfactant are mixed in the mannerfully disclosed in U.S. Pat. No. 5,458,769 or 5,496,486, the entiredisclosure of both are incorporated herein by reference.

In another embodiment, a minor amount, up to about 5%, of a silica suchas a silicon dioxide hydrate is mixed with the alkali metal carbonateprior to loading with the nonionic surfactant. A variety of siliceoussubstances are acceptable for addition to the detergent composition,although highly absorbent silica of the precipitated or fumed variety ispreferred. The preferred siliceous compounds have oil absorption numbersof 150 to about 350 or greater, preferably about 250 or greater. Asexamples of operable silicas, the following siliceous material arerepresentative: Sipernat 50, Syloid 266, Cabosil M-5, Hisil 7-600.Preferably, from about 0.5% to about 4% by weight of the final product,of silica is mixed with the alkali metal carbonate prior to loading bythe nonionic surfactant. More preferably, from about 3% to about 4% ofsilica by weight of the final product is mixed with the alkali metalcarbonate.

Low levels of carboxymethylcellulose, for example from about 0.1% up toabout 5%, to aid in the prevention of soil suspended in the wash liquorfrom depositing onto cellulosic fabrics such as cotton, may also bemixed with the alkali metal carbonate prior to loading with the nonionicsurfactant. Preferably, from about 1% to about 3%, more preferably fromabout 2% to about 3% of carboxymethylcellulose is mixed with the alkalimetal carbonate prior to loading with the nonionic surfactant. In apreferred embodiment, both the silica and the carboxymethylcellulose aremixed with the sodium carbonate prior to being loaded with the nonionicsurfactant.

The second essential ingredient is a detergent surfactant and isselected from the group consisting of anionics, nonionics,zwitterionics, ampholytics, cationics, and mixtures thereof. Thedetergent surfactant used in the present invention may be any of theconventional materials of this type which are very well known and fullydescribed in the literature, for example in “Surface Active Agents andDetergents” Volumes I and II by Schwartz, Perry & Berch, in “NonionicSurfactants” by M. J. Schick, and in McCutcheon's “Emulsifiers &Detergents,” each of which are incorporated herein in their entirety byreference. The surfactant is present at a level of from about 1% toabout 90%. Desirably, the surfactant is present at a level of from about10% to about 50%, and preferably, the surfactant is included in anamount from about 20% to about 40%.

Useful anionic surfactants include the water-soluble salts of the higherfatty acids, i.e., soaps. This includes alkali metal soaps such as thesodium, potassium, ammonium, and alkyl ammonium salts of higher fattyacids containing from about 8 to about 24 carbon atoms. Soaps can bemade by direct saponification of fats and oils or by the neutralizationof free fatty acids. Particularly useful are the sodium and potassiumsalts of the mixtures of fatty acids derived from coconut oil andtallow, i.e., sodium or potassium tallow and coconut soap.

Useful anionic surfactants also include the water-soluble salts,preferably the alkali metal, ammonium and alkylolammonium salts, oforganic sulfuric reaction products having in their molecular structurean alkyl group containing from about 8 to about 20 carbon atoms and asulfonic acid or sulfuric acid ester group. Included in the term “alkyl”is the alkyl portion of acyl groups. Examples of this group of syntheticsurfactants are the sodium and potassium alkyl sulfates, especiallythose obtained by sulfating the higher primary or secondary alcohols(C₈-C₁₈ carbon atoms) such as those produced by reducing the glyceridesof tallow or coconut oil; and the sodium and potassium alkylbenzenesulfonates in which the alkyl group contains from about 10 to about 16carbon atoms, in straight chain or branched chain configuration, e.g.,see U.S. Pat. No. 2,220,099 and alkylbenzene sulfonates in which theaverage number of carbon atoms in the alkyl group is from about 11 to14, abbreviated as C₁₁₋₁₄ LAS.

The anionic surfactants useful in the present invention may also includethe potassium, sodium, calcium, magnesium, ammonium or loweralkanolammonium, such as triethanolammonium, monoethanolammonium, ordiisopropanolammonium paraffin or olefin sulfonates in which the alkylgroup contains from about 10 to about 20 carbon atoms. The lower alkanolof such alkanolammonium will normally be of 2 to 4 carbon atoms and ispreferably ethanol. The alkyl group can be straight or branched and, inaddition, the sulfonate is preferably joined to any secondary carbonatom, i.e., the sulfonate is not terminally joined.

The anionic surfactants useful in the present invention may also includethe potassium, sodium, calcium, magnesium, ammonium or loweralkanolammonium, such as triethanolammonium, monoethanolammonium, ordiisopropanolammonium paraffin or olefin sulfonates in which the alkylgroup contains from about 10 to about 20 carbon atoms. The lower alkanolof such alkanolammonium will normally be of 2 to 4 carbon atoms and ispreferably ethanol. The alkyl group can be straight or branched and, inaddition, the sulfonate is preferably joined to any secondary carbonatom, i.e., the sulfonate is not terminally joined.

Other anionic surfactants that may be useful in the present inventioninclude the secondary alkyl sulfates having the general formula

wherein M is potassium, sodium, calcium, or magnesium, R₁, represents analkyl group having from about 3 to about 18 carbon atoms and R₂represents an alkyl group having from about 1 to about 6 carbon atoms.Preferably, M is sodium, R₁ is an alkyl group having from about 10 toabout 16 carbon atoms, and R₂ is an alkyl group having from about 1 toabout 2 carbon atoms.

Other anionic surfactants useful herein are the sodium alkyl glycerolether sulfonates, especially those ethers of higher alcohols derivedfrom tallow and coconut oil; sodium coconut oil fatty acid monoglyceridesulfonates and sulfates; sodium or potassium salts of alkyl phenolethylene oxide ether sulfates containing from about 1 to about 10 unitsof ethylene oxide per molecule and wherein the alkyl group contains fromabout 10 to about 20 carbon atoms.

The ether sulfates useful in the present invention are those having theformula RO(C₂H₄O)_(x)SO₃M wherein R is alkyl or alkenyl having fromabout 10 to about 20 carbon atoms, x is 1 to 30, and M is awater-soluble cation preferably sodium. Preferably, R has 10 to 16carbon atoms. The alcohols can be derived from natural fats, e.g.,coconut oil or tallow, or can be synthetic. Such alcohols are reactedwith 1 to 30, and especially 1 to 12, molar proportions of ethyleneoxide and the resulting mixture of molecular species is sulfated andneutralized.

Other useful anionic surfactants herein include the water-soluble saltsof esters of alpha-sulfonated fatty acids containing from about 6 to 20carbon atoms in the fatty acid group and from about 1 to 10 carbon atomsin the ester group; water-soluble salts of 2-acyloxyalkane-1-sulfonicacids containing from about 2 to 9 carbon atoms in the acyl group andfrom about 9 to about 23 carbon atoms in the alkane moiety;water-soluble salts of olefin and paraffin sulfonates containing fromabout 12 to 20 carbon atoms; and beta-alkyloxy alkane sulfonatescontaining from about 1 to 3 carbon atoms in the alkyl group and fromabout 8 to 20 carbon atoms in the alkane moiety.

Another example of anionic surfactants that may be useful in the presentinvention are those compounds that contain two anionic functionalgroups. These are referred to as di-anionic surfactants. Suitabledi-anionic surfactants are the disulfonates, disulfates, or mixturesthereof which may be represented by the following formula:

R(SO₃)₂M₂,R(SO₄)₂M₂,R(SO₃)(SO₄)M₂

where R is an acyclic aliphatic hydrocarbyl group having 15 to 20 carbonatoms and M is a water-solubilizing cation, for example, the C₁₅ to C₂₀dipotassium-1,2-alkyldisulfonates or disulfates, disodium 1,9-hexadecyldisulfates, C₁₅ to C₂₀ disodium 1,2-alkyldisulfonates, disodium1,9-stearyldisulfates and 6,10-octadecyidisulfates.

The nonionic detergent surfactant may be any of the conventionalmaterials of this type which are very well known and fully described inthe literature, for example in “Surface Active Agents and Detergents”Volumes I and II by Schwartz, Perry & Berch, “Nonionic Surfactants” byM. J. Schick, and McCutcheon's “Emulsifiers & Detergents,” eachincorporated herein by reference. For example, the nonionic materialsmay include compounds produced by the condensation of alkylene oxidegroups (hydrophilic in nature) with an organic hydrophobic compound,which may be aliphatic or alkyl aromatic in nature. The length of thepolyoxyalkylene group which is condensed with any particular hydrophobicgroup can be readily adjusted to yield a water-soluble compound havingthe desired degree of balance between hydrophilic and hydrophobicelements.

Other useful nonionic surfactants include the polyoxyethylene orpolyoxypropylene condensates of aliphatic carboxylic acids, whetherlinear- or branched-chain and unsaturated or saturated, containing fromabout 8 to about 18 carbon atoms in the aliphatic chain andincorporating from 5 to about 50 ethylene oxide or propylene oxideunits. Suitable carboxylic acids include “coconut” fatty add (derivedfrom coconut oil) which contains an average of about 12 carbon atoms,“tallow” fatty acids (derived from tallow-class fats) which contain anaverage of about 18 carbon atoms, palmitic acid, myristic acid, stearicacid and lauric acid.

The nonionic surfactants can also include polyoxyethylene orpolyoxypropylene condensates of aliphatic alcohols, whether linear orbranched chain and unsaturated or saturated, containing from about 8 toabout 24 carbon atoms and incorporating from about 5 to about 50ethylene oxide or propylene oxide units. Suitable alcohols include thecoconut fatty alcohol, tallow fatty alcohol, lauryl alcohol, myristylalcohol, and oleyl alcohol.

Alkyl saccharides may also find use in the composition. In general, thealkyl saccharides are those having a hydrophobic group containing fromabout 8 to about 20 carbon atoms, preferably from about 10 to about 16carbon atoms, and a polysaccharide hydrophillic group containing fromabout 1 (mono) to about 10 (poly), saccharide units (e.g., galactoside,glucoside, fructoside, glucosyl, fructosyl, and/or galactosyl units).Mixtures of saccharide moieties may be used in the alkyl saccharidesurfactants. Preferably, the alkyl saccharides are the alkyl glucosideshaving the formula

R¹O(C_(n)H_(2n)O)_(t)(Z)_(x)

wherein Z is derived from glucose, R¹ is a hydrophobic group selectedfrom the group consisting of alkyl, alkyl-phenyl, hydroxyalkyl,hydroxyalkylphenyl, and mixtures thereof in which the alkyl groupscontain from about 10 to about 18 carbon atoms, n is 2 or 3, t is from 0to about 10, and x is from 1 to about 8. Examples of such alkylsaccharides are described in U.S. Pat. No. 4,565,647 (at col. 2, line 25through col. 3, line 57) and U.S. Pat. No. 4,732,704 (at col. 2, lines15-25), the pertinent portions of each are incorporated herein byreference.

Semi-polar nonionic surfactants include water-soluble amine oxidescontaining one alkyl moiety of from about 10 to 18 carbon atoms and twomoieties selected from the group of alkyl and hydroxy alkyl moieties offrom about 1 to about 3 carbon atoms; water-soluble phosphine oxidescontaining one alkyl moiety of about 10 to 18 carbon atoms and twomoieties selected from the group consisting of alkyl groups and hydroxyalkyl groups containing from about 1 to 3 carbon atoms; andwater-soluble sulfoxides containing one alkyl moiety of from about 10 to18 carbon atoms and a moiety selected from the group consisting of alkyland hydroxy alkyl moieties of from about 1 to 3 carbon atoms.

Ampholytic surfactants include derivatives of aliphatic or aliphaticderivatives of heterocyclic secondary and tertiary amines in which thealiphatic moiety can be straight chain or branched and wherein one ofthe aliphatic substituents contains from about 8 to 18 carbon atoms andat least one aliphatic substituent contains an anionicwater-solubilizing group.

Zwitterionic surfactants include derivatives of aliphatic, quaternary,ammonium, phosphonium, and sulfonium compounds in which one of thealiphatic substituents contains from about 8 to 18 carbon atoms.

Cationic surfactants can also be included in the present detergent.Cationic surfactants comprise a wide variety of compounds characterizedby one or more organic hydrophobic groups in the cation and generally bya quatemary nitrogen associated with an acid radical. Pentavalentnitrogen ring compounds are also considered quatemary nitrogencompounds. Halides, methyl sulfate and hydroxide are suitable. Tertiaryamines can have characteristics similar to cationic surfactants atwashing solution pH values less than about 8.5. A more completedisclosure of these and other cationic surfactants useful herein can befound in U.S. Pat. No. 4,228,044, Cambre, issued Oct. 14, 1980,incorporated herein by reference.

The ethoxylated alkyl phenols with C₈-C₁₆ alkyl groups, preferably C₈-C₉alkyl groups and from about 4-12 EO units per molecule, or ethoxylatedfatty acid amides may be used. Other nonionic detergent compounds whichcan be used for the purposes of the present invention will be readilyapparent to those skilled in the art. It will be appreciated that thenonionic compounds which are used to the greatest benefit are liquidcompounds which are more difficult to incorporate into detergentcompositions otherwise, though pasty or solid nonionic detergentcompounds may also be used. In the latter case, adsorption of thenonionic compound onto the calcium carbonate may be facilitated by theuse of elevated temperatures.

Preferably, the nonionic surfactant is a polyoxyethylene orpolyoxypropylene condensate of an aliphatic alcohol, whether linear- orbranched-chain and unsaturated or saturated, containing from about 8 toabout 24 carbon atoms and incorporating from about 5 to about 50ethylene oxide or propylene oxide units. The nonionic detergentcompounds of most commercial interest and which are most readilyavailable include the ethoxylated synthetic or natural fatty alcohols,preferably linear primary or secondary monohydric alcohols with C₈-C₁₈,preferably C₁₀-C₁₆, alkyl groups and about 3-80, preferably 5-20,ethylene oxide (EO) units per molecule.

Examples of the preferred nonionic surfactant compounds in this categoryare the nonionic surfactants having the formula R¹(OC₂H₄)_(n)OH, whereR¹ is a C₈-C₁₆ alkyl group or a C₈-C₁₂ alkyl phenyl group, and n is from3 to about 80. Particularly preferred nonionic surfactants are thecondensation products of C₈-C₁₆ alcohols with from about 5 to about 20moles of ethylene oxide per mole of alcohol, e.g., a C₁₂-C₁₆ alcoholcondensed with about 5 to about 9 moles of ethylene oxide per mole ofalcohol. Nonionic surfactants of this type include the NEODOL™ products,e.g., Neodol 23-6.5, Neodol 25-7, and Neodol 25-9 which arerespectively, a C₁₂₋₁₃ linear primary alcohol ethoxylate having 6.5moles of ethylene oxide, a C₁₂₋₁₅ linear primary alcohol ethoxylatehaving 7 moles of ethylene oxide, and a C₁₂₋₁₅ linear primary alcoholethoxylate having 9 moles of ethylene oxide.

The amount of a surfactant particularly a liquid nonionic surfactantthat can be adsorbed on the alkali metal carbonate to give a freeflowing product is generally up to about 50% by weight of the resultantproduct. Although higher levels of nonionic detergent surfactants can beused if desired, this tends to defeat the object of the presentinvention because the resultant product is a paste or a powder with poorflow properties. On the other hand, with very low levels of less than,say, about 5% of the nonionic detergent compound, there is clearlylittle benefit achieved.

Desirably, the ratio of alkali metal carbonate to nonionic surfactant isfrom about 2:1 to about 3.5:1. Within this range of ratios, it isbelieved that an effective cleaning free-flowing powder can be produced.Preferably, the ratio is from about 2.2:1 to about 3.3:1, morepreferably from about 2.3:1 to about 2.8:1. In the most preferredembodiment the ratio of alkali metal carbonate to nonionic surfactant isabout 2.4:1.

Preferably, the surfactant is a nonionic surfactant which isincorporated in an amount of about 5% to about 50% by weight of thefinal product. Of course, the detergent benefits of high nonionicconcentration must be balanced against cost-performance. Therefore, thepreferred range for the nonionic surfactants is from about 20% to about40% by weight of the final product, more preferably, from about 20% toabout 30%. Most preferably, the nonionic surfactant is present at alevel of about 25%. It should be mentioned that within the above rangesthe lower levels tend to be required under conditions of use at higherproduct concentrations, as is commonly the practice in Europe, and theconverse applies under conditions of use at lower productconcentrations, as tends to occur in North America and Asia.

Loading, adsorption, and absorption of the nonionic surfactant onto thealkali metal carbonate (and into its porous structure) can be achievedby simple admixture with sufficient agitation to distribute the nonioniccompound entirely on the alkali metal carbonate to form a premixcomprising a homogeneous mixture of nonionic surfactant coated alkalimetal carbonate. The loading can be accomplished in any of the knownmixers such as by a ribbon or plow blender. Preferably, the nonionicsurfactant is sprayed onto the alkali metal carbonate and other optionalingredients, if present, while they are agitated. In preparing thepremix of the present invention, it is important that the alkali metalcarbonate is sufficiently coated with the nonionic surfactant so thatwhen water is later added, the water does not immediately contactuncoated carbonate and hydrate the carbonate. It is believed thatexcessive hydration of the carbonate reduces the amount of wateravailable to solubilize the carboxylic acid which will requireadditional water to achieve the desired agglomerated particle size.

At the same time, if an excess amount of nonionic surfactant is presentin the premix, the later admixed carboxylic acid may be coated with theexcess nonionic surfactant. As a result, the amount of carboxylic acidavailable to solubilize and neutralize with the alkali metal carbonatewill be reduced, which, in turn will reduce the agglomeration efficiencyand require additional carboxylic acid to achieve the desired particlesize.

In the preferred embodiment of the present invention, from about 5% toabout 80% sodium carbonate is blended with from about 5% to about 50% ofa nonionic surfactant, wherein the nonionic surfactant is the solesurfactant present to form a form a premix comprising a homogeneousmixture of nonionic surfactant coated alkali metal carbonate. Morepreferably, the premix is formed by blending from about 20% to about 70%of sodium carbonate with up to about 5%, preferably from about 2% toabout 4% of silica, and from about 1 % to about 3% of minor detergentingredients including carboxymethylcellulose and, loading the sodiumcarbonate, silica, and carboxymethylcellulose with from about 20% toabout 40% of a nonionic surfactant wherein the nonionic surfactant isthe sole surfactant present in the premix. In a more preferredembodiment, the premix is formed by mixing from about 30% to about 65%of sodium carbonate, from about 0.5% to about 4% of a silica, from about2% to about 3% of carboxymethylcellulose, and a minor amount of otheroptional detergent ingredients; and spraying from about 20% to about 30%of a nonionic surfactant wherein the nonionic surfactant is the soledetergent surfactant present, onto the mixed carbonate, silica,carboxymethylcellulose, and optional ingredients.

As discussed above, the surfactant, particularly the nonionic surfactantis added in an amount so that it is within a particular ratio withrespect to the sodium carbonate. Within this ratio range, the surfactantadequately coats the sodium carbonate yet does not provide a substantialexcess of surfactant which would then undesirably coat the carboxylicacid. Moreover, it is believed that the order of addition is importantto achieving the desired agglomeration. By loading the alkali metalcarbonate with the surfactant prior to the admixture of carboxylic acidand introduction of water, the desired particle size is achieved whilestill producing a free-flowing powder.

The third essential ingredient in the free-flowing agglomerated powderdetergent composition of the present invention is the alkali metal saltof a carboxylic acid wherein the carboxylic acid is selected from thosecarboxylic acids that, below a first temperature, have a greater watersolubility than the water solubility of its corresponding alkali-metalsalt. Preferably, the alkali metal carboxylate is provided solely by thereaction of the corresponding carboxylic acid and the alkali metalcarbonate. Preferred alkali metal carboxylates are selected from thegroup consisting of alkali metal citrate, alkali metal malate, andmixtures thereof. Alkali metal citrate is the most preferred becausecitric acid is relatively inexpensive and is readily obtainable. In thepreferred embodiment where the alkali metal carbonate is sodiumcarbonate, the alkali metal carboxylate is selected from the groupconsisting of sodium citrate, sodium malate, and mixtures thereof.

The alkali metal carboxylate is present in the detergent composition ata level of up to about 25%, preferably from about 4% to about 18% and isprovided solely by the reaction of the carboxylic acid corresponding tothe alkali metal carboxylate, and the alkali metal carbonate. It isbelieved that when the amount of alkali metal carboxylate is within thisrange, the desired agglomeration of the nonionic surfactant loadedalkali metal carbonate will be efficiently achieved and will produce thedesired particle size. More preferably, the alkali metal carboxylate ispresent at a level of from about 5% to about 13% and in the mostpreferred embodiment is present at a level of about 9% to about 11%.

Desirably, as will be further discussed below, the carboxylic acidshould be substantially completely neutralized by reaction with thealkali metal carbonate to its corresponding alkali metal salt duringprocessing. For example, malic acid should be substantially completelyneutralized to an alkali metal malate. Because of reaction andprocessing limitations, it is believed that the carboxylic acid is notcompletely neutralized. Therefore, it is desirable to neutralize atleast about 90%, preferably at least about 95% and more preferably atleast about 99% of the carboxylic acid to its alkali metal carboxylate.Preferably, the substantially completely neutralized carboxylic acidwill be selected from the group consisting of the alkali metal salts ofcitric acid, malic acid, and mixtures thereof. In the preferredembodiment where the alkali metal carbonate is sodium carbonate, thesubstantially completely neutralized carboxylic acid is selected fromthe group consisting of sodium citrate, sodium malate, and mixturesthereof.

The amount of carboxylic acid to be admixed can be determined from theamount of substantially completely neutralized carboxylic acid desiredin the final product as well as the amount of alkali metal carbonatepresent. It would be desirable to use the minimum amount of carboxylicacid necessary to achieve acceptable agglomeration. This amount,however, must be balanced against the desire to provide an amount of thealkali metal carboxylate in the final product sufficient to control hardwater filming in those instances where hard water is used. Acid levelswhich are too high can result in lower alkalinity by neutralization ofthe alkali metal carbonate which can detrimentally affect detergentperformance. Too little acid, on the other hand, reduces the ability ofthe acid salt hydrate to entrap the added moisture and hampersagglomeration. The carboxylic acid is therefore incorporated in anamount such that the ratio between the alkali metal carbonate and thecarboxylic acid is in the range from about 6.5:1 to about 12:1,preferably in the range from about 6.5:1 to about 8:1, more preferablyabout 7:1.

The carboxylic acid is admixed with the premix at a level of up to about18% by weight of the final product. The preferred range of admixed acidis from about 3% to about 13% by weight of the final product, morepreferably from about 4% to about 10% and most preferably from about 7%to about 9%. The carboxylic acid is only lightly admixed with the premixprior to the later introduction of water to minimize the potential forcoating of the carboxylic acid by the nonionic surfactant.

After the carboxylic acid is lightly admixed with the premix, a smallamount of water is incorporated to accomplish agglomeration of theparticles. The water may be incorporated as a mist, steam, or in anothersuitable fashion. Desirably, the amount of water used is as small aspractical in order to minimize subsequent drying time, energy and thuscost. The water is therefore incorporated at a level from about 0.1% tono more than about 7%, preferably no more than about 5%. In a morepreferred embodiment, the water is incorporated in a range between about4% and about 5%.

The water is incorporated into the mixture using any suitable mixingapparatus to achieve agglomeration of the mixture. Preferably, a drumagglomerator is used. The agglomerator rotates to distribute the mixturealong the length of the drum as the falling sheets of the mixture aresprayed with water to produce a well controlled agglomeration of theparticles.

Without wishing to be bound by any particular theory, it is believedthat the carboxylic acid is solubilized and neutralized by the alkalimetal carbonate at the same time the alkali metal carbonate is hydrated.The carboxylic acid should be substantially completely neutralized toits corresponding alkali metal salt which, below a first temperature, isless water soluble than the acid form. During the neutralization of thecarboxylic acid, the alkali metal carboxylate binds the surfactantcoated alkali metal carbonate particles to agglomerate them and toproduce the desired particle size. As the drum rotates and the particlesare agglomerated, the larger particles move from the inlet end to theoutlet end of the agglomerator where they exit and are conveyed to adryer to remove the free water from the agglomerated particles. Theagglomerator is preferably inclined from the inlet to the outlet so thatas the particles agglomerate, the larger agglomerated particles movefrom the inlet end to the outlet end where they are dried.

In particular, while not wishing to be held to a specific theory, it isbelieved that the carboxylic acid is solubilized with the water andreacts with the alkali metal carbonate to become substantiallycompletely neutralized. The salts of the carboxylic acids, for example,citric and malic, have a water solubility less than their acid formbelow a first temperature and therefore the salts come out of solutionto bind and thus agglomerate the particles. As noted above, insufficientcoating by the surfactant on the surface of the alkali metal carbonatewill produce excessive hydration of the sodium carbonate. As a result,the water required to solubilize the carboxylic acid will not beavailable and additional water and processing time will be required toproduce the desired agglomerated particle size. In addition, hydrationof sodium carbonate is exothermic and excessive hydration of sodiumcarbonate will generate undesirable heat and increase the temperature ofthe mixture above the first temperature. At the same time, an excess ofsurfactant present in the premix may cause coating of the carboxylicacid resulting in a reduction of agglomeration efficiency. In addition,additional carboxylic acid and water may be required to achieve thedesired agglomerated particle size. Consequently, the order of additionas well as the temperature are believed to be important to achieving thedesired agglomeration and particle size.

It is believed that by adding the carboxylic acid after the premix hasbeen formed, the desired solubilization of the carboxylic acid isachieved prior to a substantial reaction with the alkali metalcarbonate. If the citric acid were admixed with the alkali metalcarbonate prior to adding the surfactant, it is believed that theresulting product would not achieve the desired free flowing anddissolution properties.

As noted above, the preferred carboxylic acid has a greater watersolubility than its corresponding alkali metal salt below a firsttemperature. An increase in temperature above the first temperaturetherefore adversely affects the relative solubility of the acid form ofthe carboxylic acid in comparison to the salt form which, in turn,adversely affects the agglomeration efficiency. As a result, theformation of the alkali metal salt of the carboxylic acid is controlledso as to prevent the temperature of the mixture from rising above thefirst temperature.

Generally, the first temperature can range from about 15° C. to about40° C., preferably from about 32° C. to about 35° C. A first temperaturehigher than about 42° C. appears to adversely affect the productcharacteristics and is, therefore, undesirable.

It will be understood by one skilled in the art that several factors canbe varied to control the residence time (i.e., the weight of the mixtureon the bed divided by the total feed rate) and agglomerate size, e.g.,feed rate to the drum, angle of the drum, rotational speed of the drum,the number and location of the water spray. The result of manipulatingsuch factors is desired control of the particle size and density of theagglomerates.

The wetted agglomerated particles are dried to remove any free water.The drying may be accomplished by any known method such as by a tumblingdryer or air drying on a conveyor. As one skilled in the art willappreciate, the time, temperature, and air flow may be adjusted toprovide for an acceptable drying rate. Using a high ambient temperaturein the dryer can shorten the residence time in the dryer, while lowertemperatures may unduly lengthen the residence time. Short residencetimes, however, may increase the risk of adversely affecting thestability of the agglomerates or of incompletely drying the agglomerate.

It is desirable to remove as much water as practicable since thepresence of water, even when bound, may detrimentally react withpost-added moisture sensitive detergent ingredients such as bleaches andenzymes. In addition, the presence of water may, over time and undertypical storage conditions, cause product caking. Therefore, in apreferred embodiment, a minor amount of water is added to accomplishagglomeration and furthermore, at least about 50% of the added water isremoved by drying. More preferably, at least about 60% of the addedwater is removed by drying. Consequently, the resulting compositioncontains less than about 3% of bound water, more preferably less thanabout 2% of bound water.

The dried particles have an average particle mesh size of up to about 20U.S. Standard Sieve number. Preferably, the particles have a particlemesh size such that about 90% of the particles are in the range fromabout 20 to about 100 U.S. Standard Sieve number. The resulting powderhas a bulk density of at least 0.7 g/cc, preferably from about 0.8 toabout 0.9 g/cc, more preferably from about 0.85 to about 0.9 g/cc.

The mixing steps in the process to prepare the detergent compositions ofthis invention can be accomplished with a variety of mixers known in theart. For example, simple, paddle or ribbon mixers are quite effectivealthough other mixers, such as drum agglomerators, fluidized beds, panagglomerators and high shear mixers may be used.

The preferred embodiment of the agglomerated detergent composition ofthe present invention includes from about 20% to about 70% of sodiumcarbonate, from about 20% to about 40% of a surfactant, particularly anonionic detergent surfactant and from about 3% to about 13% of a sodiumcarboxylate selected from the group consisting of sodium citrate, sodiummalate, and mixtures thereof, wherein the sodium carboxylate is providedsolely by the reaction, at a temperature, below a first temperature, or(a) a premix comprising a surfactant and sodium carbonate, (b) acarboxylic acid selected from the group consisting of citric acid, malicacid, and mixtures thereof, and (c) water.

Preferably, the agglomerated detergent composition resulting from theprocess of the present invention includes from about 20% to about 70% ofsodium carbonate, from about 20% to about 40% of a nonionic detergentsurfactant, wherein the nonionic surfactant is the sole detergentsurfactant present, and from about 4% to about 18% of a sodium salt of acarboxylic acid selected from the group consisting of sodium citrate,sodium malate, and mixtures thereof, wherein the sodium salt of thecarboxylic acid is formed by the reaction at a temperature below a firsttemperature of (a) a premix comprising a nonionic surfactant loadedsodium carbonate, (b) a carboxylic acid selected from the groupconsisting of citric acid, malic acid, and mixtures thereof, and (c)water.

In addition to the essential ingredients mentioned above, it is possibleto include in the detergent composition of the invention otherconventional detergent additives. Examples of such optional additivesare lather boosters such as alkanolamides, particularly themonoethanolamides derived from palm kernel fatty acids and coconut fattyacids, lather depressants such as alkyl phosphates and silicone oils,anti-redeposition agents such as sodium carboxymethyl cellulose, oxygenreleasing bleaching agents such as sodium perborate and sodiumpercarbonate, peracid bleach precursors, chlorine releasing bleachingagents such as trichloroisocyanuric acid and alkali metal salts ofdichloroisocyanuric acid, fabric softening agents, inorganic salts suchas sodium sulfate, anti-tarnish and anticorrosion agents, soilsuspending agents, soil release agents and, usually present in veryminor amounts, fluorescent agents, perfumes, enzymes, enzyme stabilizingagents and germicides. These optional additives may be added whenconvenient during or after, preferably after, the drying of thedetergent compositions of the present invention. Such ingredients aredescribed in U.S. Pat. No. 3,936,537, incorporated herein by reference.

A low level of silicate, for example up to about 5% by weight, isusually advantageous in decreasing the corrosion of metal parts infabric washing machines. Useful silicates such as an alkali metalsilicate, particularly sodium neutral, alkaline, meta- or orthosilicatecan be used.

Water-soluble, organic builders may also find use in the detergentcomposition of the present invention. For example, the salts ofethylenediaminetetraacetic acid, nitrilotriacetic acid, oxydisuccinicacid, mellitic acid, benzene polycarboxylic acid, polyacrylic acid, andpolymaleic acid may be included.

Aluminosilicate ion exchange materials may be useful in the detergentcomposition of this invention and may include the naturally-occurringaluminosilicates or synthetically derived. a method for producingaluminosilicate ion exchange materials is discussed in U.S. Pat. No.3,985,669, incorporated herein by reference. Such synthetic crystallinealuminosilicate ion exchange materials are available under thedesignations Zeolite A, Zeolite B, and Zeolite X. In addition, layeredor structured silicates such as those sold under the designation SKS-6by Hoechst-Celanese may also find use in the detergent composition.

Bleaching agents and activators that may find use in the presentdetergent composition are described in U.S. Pat. Nos. 4,412,934, and4,483,781, both of which are incorporated herein by reference. Suitablebleach compounds include sodium perborate, sodium percarbonate, etc. andthe like, and mixtures thereof. The bleach compounds may also be used incombination with an activator such as, for example,tetra-acetyl-ethylenediamine (TAED), sodium nonanoyloxybenzene sulfonate(SNOBS), diperoxydodecanedioc acid (DPDDA) and the like, and mixturesthereof. Chelating agents are described in U.S. Pat. No. 4,663,071, fromcolumn 17, line 54 through column 18, line 68, incorporated herein byreference. Suds modifiers are also optional ingredients and aredescribed in U.S. Pat. Nos. 3,933,672, and 4,136,045, both incorporatedherein by reference.

Smectite clays may be suitable for use herein and are described in U.S.Pat. No. 4,762,645, at column 6, line 3 through column 7, line 24,incorporated herein by reference. Other suitable additional detergencybuilders that may be used herein are enumerated in U.S. Pat. No.3,936,537, column 13, line 54 through column 16, line 16, and in U.S.Pat. No. 4,663,071, both incorporated herein by reference.

In addition, whitening agent particles may be added to the dried powderdetergent described above. The whitening agent particles comprise afluorescent whitening agent and an anionic surfactant that substantiallyprotects the whitening agent from degradation caused by the presence ofnonionic surfactant. The preferred whitening agent particle compositionand method of making it more fully described in U.S. patent applicationSer. No. 08/616,570 now U.S. Pat. No. 5,714,452 and U.S. patentapplication Ser. No. 08/616,208 now U.S. Pat. No. 5,714,456,respectively, both of which are incorporated herein by reference.

The laundry detergent compositions of the present invention can beformulated to provide a pH (measured at a concentration of 1% by weightin water at 20° C.) of from about 7 to about 11.5. A pH range of fromabout 9.5 to about 11.5 is preferred for best cleaning performance.

The detergent composition may also contain a post-added acidulant forimproved solubility, as more particularly described in U.S. applicationSer. No. 08/617,941 now abandoned the entire disclosure of which isincorporated herein by reference.

The following examples are for illustrative purposes only and are not tobe construed as limiting the invention.

EXAMPLE 1

The ingredients listed in Table 1 were agglomerated into an acceptablefreeflowing powder detergent in the following manner. The sodiumcarbonate, whitener, silica, and carboxymethylcellulose were mixed forabout 1 minute in a ribbon mixer to achieve a uniform mixture. Neodol25-7 (a C₁₂-C₁₅ alcohol ethoxylated with 7 moles of ethylene oxide) waspoured into the above mixture while mixing to uniformly coat the sodiumcarbonate and other ingredients. The loaded sodium carbonate (and otheringredients) were transferred to a laboratory scale agglomerator(O'Brien Industrial Equip. Co., 3 foot diameter, 1 foot long) which wasrotated at about 9 rpm for about 2 minutes after which water was sprayedon the mixture to cause agglomeration of the particles. Thereafter, themixture was dried to a moisture content of about 2.15. The resultingcomposition had a bulk density of 0.85 and had a Flodex value of 12 astested in a Model No. 211, Hansen Research Corp. Flodex testingapparatus.

TABLE 1 Material Amount (weight %) Sodium Carbonate (FMC Grade 90) 55.88Brightener (Tinopal SWN) 0.02 Silica (Sipernat 50) 3.0Carboxymethylcellulose 2.0 Neodol 25-7 22.0 Citric Acid 7.5 Water(added) 4.0 Water (after drying) 1.5 Post-added fumaric acid 5.0Post-added ingredients 3.1 (fragrance, enzyme whitener)

EXAMPLES 2-4

The following ingredients were agglomerated in the same fashion asdescribed in Example 1, above, with the results also shown in Table 2.

TABLE 2 Material Amount (Formula Weight) Example No. 2 3 4 SodiumCarbonate 55.88 55.88 53.18 Silica 3.0 3.0 3.0 Carboxymethylcellulose2.0 — 2.0 Brightener 0.02 0.02 0.02 Citric Acid 7.5 7.5 7.5 Water (addedfor agglomeration) 4.0 4.0 4.0 Water (after drying) 2.2 1.2 1.2 Density0.85 0.87 0.84 Flodex 12 9 10

EXAMPLES 5-6

Table 3 lists typical amounts of ingredients useful to make afree-flowing nonionic surfactant detergent according to the presentinvention. The sodium carbonate, silica, and carboxymethylcellulose canbe mixed and, while mixing, the nonionic surfactant can be sprayed ontothe mixture to coat the mixture. The citric acid can then mixed and,while mixing, water can be sprayed onto the mixture to cause theparticles to agglomerate. The agglomerated particles can be dried.Thereafter, any post-added optional ingredients like enzymes,fragrances, and the like can be added as well as an acidulant such asfumaric acid.

TABLE 3 Materials Amount (Weight %) Example No. 5 6 Sodium Carbonate59.6 53.2 Silica 3.0 3.0 Carboxymethylcellulose 2.2 2.0 Pareth 25-7 24.722.0 Citric Acid 8.4 7.5 Water (after drying) 2.1 1.5 Optional MinorIngredients — 5.8 Post-added fumaric acid — 5.0

It should be understood that a wide range of changes and modificationscan be made to the embodiments described above. It is therefore intendedthat the foregoing description illustrates rather than limits thisinvention, and that it is the following claims, including allequivalents, which define this invention.

What is claimed is:
 1. A process for producing a free-flowingagglomerated powder detergent composition comprising the steps of: a.preparing a homogeneous surfactant coated alkali metal carbonate premixcomprising: i. from about 5% to about 80% by weight of an alkali metalcarbonate; ii. from about 5% to about 50% by weight of a detergentsurfactant, wherein the detergent surfactant is selected from the groupconsisting of anionics, nonionics, zwitterionics, ampholytics,cationics, and mixtures thereof; b. subsequently admixing a carboxylicacid with the premix to provide a mixture, wherein below a firsttemperature, which is less than about 42° C., the carboxylic acid has agreater water solubility than the water solubility of its correspondingalkali metal salt, the carboxylic acid being admixed in an amount up toabout 18% by weight; and c. subsequently adding water to the mixturewhereby the carboxylic acid solubilizes and reacts with the alkali metalcarbonate below the first temperature.
 2. The process of claim 1 whereinthe alkali metal carbonate is sodium carbonate.
 3. The process of claim1 wherein the surfactant consists of a nonionic surfactant.
 4. Theprocess of claim 3 wherein the ratio of sodium carbonate to nonionicsurfactant is in the range of about 2:1 to about 3.5:1.
 5. The processof claim 1 wherein the carboxylic acid is selected from the groupconsisting of citric acid, malic acid, and mixtures thereof.
 6. Theprocess of claim 1 wherein the amount of the carboxylic acid is suchthat the ratio of the sodium carbonate to the carboxylic acid is fromabout 6.5:1 to about 12:1.